1. Field of the Invention
The invention relates to a receiver which comprises a Surface Acoustic Wave (SAW) filter to suppress signals frequency adjacent to a desired signal. SAW filters provide good selectivity combined with a substantially constant group delay. This makes them particularly suited for use in television receivers.
The invention further relates to a filter arrangement which comprises a SAW filter and a coupling network for supplying an input signal to the SAW falter.
2. Description of the Related Art
The "Kokai" publication No. 2-237,211 describes a filter arrangement which, in principle, can be used in a television receiver. The Figure accompanying the English abstract of this publication, which shows the prior art filter arrangement, constitutes FIG. 1 of this specification.
In the prior art filter arrangement, a coupling network 14 is coupled in series with a SAW filter constituted by a piezoelectric substrate 11 on which an input electrode 12 and an output electrode 13 are placed. The coupling network 14 comprises an inductor 16 coupled in parallel to the two input terminals of the SAW filter. The inductor 16 is chosen such that it cancels the capacitance of the electrode 12. Furthermore, a series resonance circuit, formed by an inductor 17 and a capacitor 18, is coupled in series with one of the input terminals. In the cited "Kokai" publication, it is claimed that this filter arrangement has a favorable insertion loss when properly dimensioned.
However, it has been proven in practice that a television receiver equipped with the prior art filter arrangement performed unsatisfactorily.